This invention relates to an improvement in a device used to measure moisture in a substrate. More particularly the invention resides in an improvement to a moisture dermatometer as described in U.S. Pat. No. 4,013,065.
A moisture dermatometer is a device for measuring the moisture content of human skin (the statrum corneum). For cosmetic or other purposes, it is desirable to be able to determine the moisture in the skin. The measurement of the moisture content of the stratum corneum requires an instrument which is sensitive over a small range of skin depth. The stratum corneum is surrounded on one side by the outside environment with relatively low moisture content, and on the other side by the deeper layers of the skin with much higher moisture content.
The ideal instrument should sense moisture only in this narrow region. The moisture dermatometer of U.S. Pat. No. 4,013,065 uses a stray field capacitor to sense changes in the dielectric constant of the outer layer of the skin which is directly influenced by its moisture content, said device also incorporates an A.C. voltage divider technique whereby changes in the capacitance of the stray field capacitor are reflected as amplitude modulation of a carrier waveform. However, several deficiencies are evident when this technique is employed, for example: (a) the amplitude modulation sensitivity to noise reduces the reproducability of the readings; (b) the output signal being inversely proportional to moisture content, thus requiring that the output signal be processed further to provide a reading that would directly reflect an increase in moisture content; and (c) the inability to obtain a reading at a predetermined time interval after contact with the skin.
The instant invention provides an improvement means to overcome each of the aforesaid shortcomings.